"That, along with longer opening hours, may well mitigate this for some people," Mr Alcorn said.
"We are available to people to help mediate with the bank and act on their behalf. There will be people who, if they can't get benefit, will be badly stuck.
"For an organisation the size of RBS there should have been an automatic business continuity plan or back-up."
Mr Alcorn said the CAB was available to help anyone having difficulties because of the bank failure.
Ulster Bank said extra staff had been drafted in to answer queries and resolve any financial worries customers may have had.
The bank has apologised again to customers affected.